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Environmental Noise

End. Environmental Noise. Self Learning Package. Department of Building Services Engineering. The Hong Kong Polytechnic University. Next. Home. Help. Acknowledgements. Previous. Next. Home. Help. Preface.

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Environmental Noise

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  1. End Environmental Noise Self Learning Package Department of Building Services Engineering The Hong Kong Polytechnic University Next

  2. Home Help Acknowledgements Previous Next

  3. Home Help Preface • This teaching material concerns the measurement, assessment and prediction of traffic noise in Hong Kong. • In the measurement section, the conventional procedure and the equipment required will be introduced. • There are several traffic noise prediction schemes in existing literature, but the Hong Kong Government in general has adopted the scheme called “Calculation of Road Traffic Noise (CRTN)” for noise impact assessment which required prediction. A simplified version of this scheme will be introduced. A noise level calculator is also developed for your experiment. • The current statutory noise control strategy is also introduced. Site Map Previous Next

  4. Home Help Experience the Traffic Noise • Before going into the material, let click “Video” to experience traffic noise. • At the same time, please take note of the different type of vehicles running on the road and try to appreciate the loudness of the corresponding noise as far as possible. Video Previous Next

  5. Home Help Environmental Noise Measurement Prediction Noise Limits References Site Map Previous

  6. Contents Help When Where What Traffic Noise Measurement Instruments Records

  7. Traffic Noise Measurement Contents Where to measure? • Above the ground - At a position 1.2 m above the ground without any reflecting surfaces (other than ground) within 15m from the microphone. - Unobstructed to the road under concern. • Outside the building - Normally at a position 1 m from the exterior of the building façade. Back

  8. Traffic Noise Measurement Contents What to measure? • Commonly used noise parameters in local practice are: • LAeq,LAFN, LAFmax; • Other parameters: • Traffic volume; • Vehicle speed; • Weather condition; and • Road surface condition. Back

  9. What to measure? Contents Noise parameter (1/3) A-weighted equivalent continuous sound pressure level, LAeq,T . where pA(t) is the A-weighted instantaneous sound pressure at running time t. p0 is the reference sound pressure (=20mPa) T is the duration of measurement. Back Next

  10. What to measure? Contents Noise parameter (2/3) N percent exceedance level, LAFN,T • F-Time-weighted and A-frequency-weighted sound pressure level that is exceeded for N % of the time interval T considered. • e.g. LAF10,1h, LAF50,1h, LAF90,1h, etc. Back Previous Next

  11. What to measure? Contents Noise parameter (3/3) Maximum time-weighted and frequency-weighted sound pressure level, LAFmax Greatest F-time-weighted and A-frequency-weighted [5] sound pressure level within a stated time interval. Back Previous

  12. What to measure? Contents Other Parameters (1/4) Traffic Volume • Peak traffic for some of the major roads can be found from traffic census [10]; • Count the number of light and heavy vehicles as defined in the CRTN [1]for each bound of the carriagewayduring the noise measurement. - Light vehicle:  1,525 kg unladen weight - Heavy vehicle: > 1,525 kg unladen weight • Traffic Volume below 200 vehicles/hour required adjustment (para13.3)[1]. Back Next

  13. What to measure? Contents Other Parameters (2/4) Vehicle Speed • Average speed for each vehicle type in each carriageway (kph); • Estimate from the time required for a vehicle travelling through a known distance (e.g. Lamppost ~ 40 m, or measurement of two landmarks); • Use of radar speed gun (with limitations). Back Previous Next

  14. What to measure? Contents Other Parameters (3/4) Weather Condition – Local Practice [2] • All conditions except rainy; and • Average wind speed is not more than 2 m/s in the direction from the road surface to the receiver; and • Wind speed at the microphone in any direction should not exceed 10 m/s. When Necessary • Refer to the calculations in ISO 9613-1 [8]& 9613-2 [9] for metrological corrections. Back Previous Next

  15. What to measure? Contents Other Parameters (4/4) Road Surface Condition – Local Practice [2] • Road surface in the measurement area is dry, because: - Acceleration of water droplets due to the tire and road surface interaction will increase the noise level; - Water will fill up the cavities of the road and reduce the sound absorption performance. Back Previous

  16. Traffic Noise Measurement Contents When to measure? Time Period [1] • Day: 0700-1900; • Evening: 1900-2300; and • Night: 2300-0700. Duration (reference time interval) [6] • 30 minutes, 1 hour, etc. Min. Measurement Period (CRTN) [1] • Tmin = (4000/q + 120/r) [minutes]; and • Tmin 5 minutes where q > 100 veh./hr, and r > 5 samples per minute. Back

  17. Traffic Noise Measurement Contents Instruments • Sound Level Meter (SLM); • Calibrator; • Extension Cable, Rod & Tripod; • Counter (Optional); • Digital Video Camera (Optional); • Stop watch (Optional); and • Radar speed gun (Optional). Back

  18. Instruments Sound Level Meter • Type I SLM [5]; • Octave band filter (optional); • Calibrated by accredited laboratory within 12 months prior to the measurement [2]; • Wind shield is to be used. Back

  19. Instruments Calibrator • Known sound pressure level at a known frequency (e.g. 94dB @ 1kHz); • Calibrated by accredited laboratory within 12 months prior to the measurement [2]; and • SLM shall be checked with the calibrator (within 1dB before and after measurement) [2]. Back

  20. Instruments Extension Cable, Rod & Tripod • Used to located the microphone at a position 1 m away from the exterior of the building façade; or • Fix the sound level meter at 1.2 m above the ground. Back

  21. Instruments Optional Counters • To count the number of vehicles for each vehicle type. Stop watches • To record the time for a vehicle passing through a known distance. Digital Video Camera • To capture the traffic conditions for all carriageways. Radar Speed Gun • To measure the speed of a vehicle. Back

  22. Traffic Noise Measurement Contents Measurement Report • Date & time of measurement; • Personnel carrying out the measurement; • Type of instrumentation used and serial numbers; • Meteorological conditions; Qualitative: rainy, drizzly, dry, wet, cloudy, sunny, etc. Quantitative (optional) [7]: wind speed & direction, thermal gradient, RH, etc. • Measurement Locations (ML); • Traffic conditions (volume and speed); • Noise Results; • Site survey photos for ML and surrounding environment; • Survey Map showing the noise ML; • Any observation made by the personnel taking the measurement. Back

  23. Traffic Noise Measurement Contents Procedures – Preparation (1/3) • Site selection; • Site visit (optional); • Determine the commencement time; • Logistics; and • Check weather forecast. Back Next

  24. Traffic Noise Measurement Contents Procedures – Measurement (2/3) • Calibration; • Erect the noise measuring system; • Setup the video recording system (optional) or count the traffic during noise measurement; • Jot down any abnormal noise event during the measurement; and • Check the data file(s) in the SLM after the measurement. Back Previous Next

  25. Traffic Noise Measurement Contents Procedures – Post-processing (3/3) • Download the data from the sound level meter; • Count the number of vehicles and estimate the vehicles speed from video (optional); and • Data analysis. Back Previous

  26. CRTN Prediction Contents CRTN Scheme (1/3) • Calculation of Road Traffic Noise scheme[1] is adopted by the local authority in assessing the noise impact from road traffic noise [2]. • Predicted Noise level is expressed in LA10,1h in local practice [3]. Next

  27. CRTN Prediction Contents Definitions (2/3) • Source of traffic noise is 0.5 m above the road surface and 3.5 m from the nearside carriageway edge, Illustration; • For distance less than 4 m away from the carriageway edge, use 4 m from the nearside instead; and • Calculations shall be worked to 0.1 dB(A) and rounded up the result for comparison. Previous Next

  28. CRTN Prediction Contents CRTN (Prediction Method) (3/3) Flow Chart A Simplified Version of CRTN • Divide the road scheme into segments • Calculate the Basic Noise level for a road segment • Correction for sound propagation • Correction for site layout • Combine contributions from segments • Example • Prediction for future noise level Previous

  29. CRTN Prediction Contents Criteria For Dividing ARoad Scheme Into Segments • Change in traffic variables, road gradient, curvature, progressive variation in screening or noise varies significantly along the length of the road; or • Noise level variation less than 2dB(A) within the same segment. Back

  30. CRTN Prediction Calculate The Basic Noise Level For A Segment BNL is obtained from: • Traffic Flow (q); • Traffic Speed (V); and • Traffic Composition (p). Plus the correction from: • Road Gradient (G), and • Road Surface. Return

  31. Calculate BNL Traffic Flow (q) • Total flow = sum of traffic flow in both carriageways • Calculate the carriageways separately when (Illustration): - separation of both carriageways > 5 m; or - height of outer edges of the carriageways > 1 m. Return

  32. Calculate BNL Suggestions For Traffic Speed (1/2) Roads not subject to a speed limit < 60 mph (100 kph), excluding slip roads. • Rural road: 108 kph • Urban road: 97 kph • All-purpose dual carriageways: 97 kph • Single carriageway > 9 m width: 88 kph • Single carriageway  9 m width: 81 kph Return Next

  33. Calculate BNL Suggestions For Traffic Speed (2/2) Roads subject to a speed limit 50 mph (80 kph) • Dual carriageways: 80 kph • Single carriageway: 70 kph Roads subject to: 30 mph < speed limit < 50 mph • Dual carriageways: 60 kph • Single carriageway: 50 kph Roads subject to a speed limit < 30 mph (50 kph) : • All carriageway: 50 kph Return Previous

  34. Correction for percentage heavy vehicles (p) is given by: Calculate BNL Traffic Composition where f is the hourly flow of heavy vehicles on a road (veh./h); and q is the total traffic flow (veh./h). Return

  35. Calculate BNL Contents BNL Calculation • BNL (V = 75kph, p = 0, G = 0) [dB(A)], Chart 2 [4] • Correction for V  75kph & p [dB(A)], Chart 4 [4] • Reduction in V (V) [kph], Chart 5[4] Back

  36. Calculate BNL Road Gradient (G) In case of carriageways treated separately or one-way traffic schemes, correction of G apply to upward flow only, [dB(A)]. where G is gradient in percentage (A/B) and up to 15% in maximum. Road Surface A B Return

  37. Calculate BNL Road Surface • For impervious bituminous and concrete road surfaces, correction for road surface, Crs = -1 dB(A) for V < 75kph. • For pervious road surfaces and low noise road surface, Crs = -3.5 dB(A) for all traffic speeds. Return Next

  38. Correction for concrete surface Correction for bituminous surface TD is the texture depth, normally TD = 1.2 is used in the local practice Calculate BNL Road Surface (V 75 kph) Return Previous

  39. CRTN Prediction Sound Propagation • The distance d’ [m] is the shortest slant distance from the effective source position for d  4 m, Assessment Point d’ h Source Road Kerb 0.5 m 3.5 m d Road Pavement Return Next

  40. Correction for distance, Cdist [dB(A)], There are provisions for Ground cover and Screening in the original CRTN scheme [1] but are not considered in this simplified version. CRTN Prediction Distance Correction Return Previous

  41. CRTN Prediction Site Layout • To calculate noise at 1 m in front of a façade, a correction (Cfac) of +2.5 dB(A) is to be made. • Reflection effect from opposite façade, side roads and size of segment are not considered in this simplified version, for details, please refer to the original CRTN scheme [1]. Return

  42. CRTN Prediction Combine ContributionsFrom All Segments • The final stage of the calculation process is to combine all the noise level contributions logarithmically to a Predicted Noise Level (PNL). where i is the contribution from each segment; N is the total number of segments and Crest are the corrections not shown in the simplified version. Return

  43. CRTN Prediction Contents Example (1/6) Site Information • The measurement site is located in Tsing Yi Island and the target road is Tsing Yi North Coastal Road. • G is about 1.7%, the road is covered with bituminous surface, separation between the carriageways is less than 5 m (site geometry), Cfac = 0 dB(A), d’ is 16 m. Back Next

  44. CRTN Prediction Contents Example (2/6) Traffic Information (from measurement). • The weather was hot and sunny with not much breeze. • The measurement was taken from 1115 to 1145. • q = 484 vehicle/hour • V = 61 kph • p = 61.5% Back Previous Next

  45. CRTN Prediction Contents Example (3/6) BNL Calculation Back Previous Next

  46. CRTN Prediction Contents Example (4/6) Corrections for road surface and façade Correction for sound propagation Predicted Noise Level Back Previous Next

  47. CRTN Prediction Contents Example (5/6) From site measurement • The LA10,30mins = 73.6 dB(A) Therefore, the discrepancy between the results from the CRTN scheme and the measurement is: 74.2 – 73.6 = 0.6 dB(A) Back Previous Next

  48. CRTN Prediction Contents Example (6/6) Remarks • Predicted value from CRTN scheme shall be rounded to the nearest whole number, i.e. LA10,1h = 74 dB(A) in this example. • Other observations in this site which relate to the CRTN scheme: - No barrier is found in this road segment. - View angle from the microphone to the road is 180. Back Previous

  49. CRTN Prediction Contents Prediction for Future Noise Level Back Next It is very common that the traffic control along a road will change in the future and thus any measurement done nowadays cannot actually reflect the noise level in the future directly. An example is the Ma On Shan T7 trunk road whose current traffic volume is more than 3 times below its design value in 2011.

  50. CRTN Prediction Contents Hiram’s Highway (1/3) Back Previous Next We use the Hiram’s Highway as an example on how the future noise level can be estimated using existing measured data. Please note the site map and we are going to predict the future noise level at M5.

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